In manufacturing the radiating fins of a radiator, heated aluminum or an alloy thereof is compressed in a mold. The known radiating fins are of two kinds, including upright radiating fins and transversal radiating fins. An assembly of transversal radiating fins 10, as shown in FIG. 1, are cut to a predetermined length after compressing. The radiating fins 11 at two opposite sides are then cut to form outwardly extending pieces 12. Each extending piece 12 is punched to form a concave opening 13 for buckling with a CPU frame (not shown). An assembly of upright radiating fins is shown in FIG. 2. After compressing, two smooth extending pieces 21 are also directly formed at two sides thereof. Then, a concave opening 22 is punched in each extending piece 21. Thus, for either transversal or upright radiating fins, a punching process is necessary, which process is both tedious and costly.